This invention relates to variable gap devices and their method of manufacture.
Variable gap devices are those which include a pair of elements and a deformable material which permits a variation in the gap between elements. In the case of variable capacitance devices, the elements are electrodes which form a capacitor. When a bias is supplied to the electrodes, the variable capacitance may be used for a wide variety of functions. For example, the deformable material may take the form of a membrane which is coupled to an electrode and displaced in response to a pressure or audio input. The variation in capacitance resulting from the change in electrode gap can be detected, and the device functions as a pressure sensor or microphone, respectively. By applying a varying bias to the electrodes, the membrane can be caused to vibrate, and the device functions as a loudspeaker or hearing aid. (See, for example, U.S. Pat. application of Busch-Vishniac et al, Ser. No. 572,683, filed Jan. 20, 1984 and assigned to Bell Telephone Laboratories now U.S. Pat. No. 4,558,184 issued Dec. 10, 1985.) Other types of variable capacitance devices make use of a flexible reflecting electrode for controlling optical interference in order to provide a display function. (See, e.g., European Patent Application Publication No. 0035299, published Sept. 9, 1981.) A still further type of device employs a deformable waveguide between two electrodes such that electrostatic attraction deforms the waveguide and attenuates light propagation therethrough. A plurality of such devices forms an optical image recorder (see, e.g., U.S. Pat. No. 4,162,118, issued to Conwell).
While devices presently available may be adequate, the need exists for a variable capacitance device which can operate at low voltages. Further, precise sensor or display operations require a highly uniform gap distance. The device should also be compact in order to be compatible with the microminiature nature of operations such as blood pressure sensors and the like.
In addition to achieving devices of the abovedescribed nature, it is desirable to provide an economical method for fabricating such devices with precise dimensions in large quantities. This requires a technique which is capable of forming gaps of the order of microns and extremely flat surfaces in a reproducible fashion. Fine-line electrode dimensions approximately 20 .mu.m in width are also desirable for many applications. Present techniques typically require difficult alignment and etching techniques which are not readily compatible with extremely small gap dimensions.
Consequently, it is an object of the invention to provide variable gap devices which are small and highly accurate, yet can be manufactured inexpensively on a large scale. It is a further object of the invention to provide a method of manufacturing such devices.